Conventionally, as an illumination device that illuminates a display panel, a direct backlight device (for example, see patent document 1) and an edge light (side light) backlight device are known.
Patent document 1 described above discloses a liquid crystal display device including a direct backlight device using a lamp (fluorescent tube) as a light source. This liquid crystal display device includes a diecast frame that supports a backlight. The diecast frame is an integral structure formed with an outer frame part that has a rising part which protrudes to the side of a liquid crystal panel and a coupling part that couples the outer frame part. In the diecast frame, a hole formation space surrounded by the outer frame part and the coupling part is formed, and a space for holding the lamp is formed by the ringing part.
In the backlight device disclosed in patent document 1, the stiffness of the diecast frame is enhanced by the rising part, and the weight thereof is reduced by the provision of the hole formation space.
Here, since the fluorescent tube is generally formed with a glass tube, when the stiffness of the frame is low, the fluorescent tube is easily broken. Hence, it is necessary to use, as the frame, a highly stiff frame, such as a diecast frame, formed with an integral structure.
However, since the diecast frame is formed by melting and pouring metal into a die, even if the its weight is reduced by the provision of the hole formation space, the weight is heavy as compared with a chassis formed by processing a metal plate or the like. Hence, in patent document 1 where the diecast frame is provided, it is difficult to further reduce the weight of the backlight device.
On the other hand, in recent years, attention has been focused on a method of using a light emitting diode (LED) as a light source instead of a fluorescent tube. In a direct backlight device using LEDs as light sources, the light sources are arranged two-dimensionally (planarly) in a position directly below a display panel. In this case, it is difficult to reduce the number of light sources so that, while the increase in the thickness of the backlight device is reduced, the uniformity of illumination light is acquired. Hence, since the light sources are closely put within an illumination region, it is necessary to use, as a backlight chassis, a box-shaped chassis having a flat surface (flat bottom portion) for retaining the light sources substantially over the entire surface.
In an edge light backlight device, a light guide plate is arranged directly below a display panel, and light sources are arranged around the light guide plate. Hence, in the edge light backlight device, as compared with the direct backlight device, it is possible to reduce the number of light sources. In the edge light backlight device, the light guide plate described above is generally formed with one member having substantially the same area as the display panel.